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Calcium carbide
From Wikipedia, the free encyclopedia
| Calcium carbide | |
|---|---|
 |
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| General | |
| Systematic name | Calcium Carbide |
| Other names | |
| Molecular formula | CaC2 |
| Molar mass | 64.1 g/mol |
| Appearance | gray-black Crystals |
| Crystal Structure | orthorhombic |
| CAS number | 75-20-7 |
| Properties | |
| Density and phase | 2.22 g/cm³, solid |
| Melting point | 2300 °C |
| Boiling point | |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Calcium carbide is a chemical compound with the chemical formula CaC2. It has the appearance of grayish white lumps. It is used mainly as a convenient source of acetylene gas.
Calcium carbide is produced in an electric arc furnace loaded with a mixture of lime and coke at about 2000 °C. Calcium carbide is formed:
- CaO + 3C→CaC2 + CO.
Calcium carbide synthesis requires an extremely high temperature, ~2000 °C, which is not practically achievable by traditional combustion, so the reaction is performed in an electric arc furnace with graphite electrodes. This reaction was an important part of the industrial revolution in chemistry that occurred as a product of massive amounts of cheap hydro-electric power liberated from Niagara Falls before the turn of the 19th century.
The reaction of calcium carbide with water was discovered by Friedrich Wohler in 1862. 1 gram of CaC2 gives 349ml of acetylene:
- CaC2 + 2 H2O → C2H2 + Ca(OH)2
This reaction is the basis of the industrial manufacture of dissolved acetylene (DA), and is one of the modern industrial uses for calcium carbide. Calcium carbide is also used as a fuel in steelmaking to extend the scrap ratio to liquid iron depending on economics. It is also used as a powerful deoxidizer at ladle treatment facilities.
Calcium carbide is used in carbide lamps, in which water drips on carbide and the formed acetylene is ignited. These lamps were of no use in coal mines where the presence of the explosive gas methane made them a serious hazard. The presence of explosive cases in coal mines led to the miner safety lamp. However carbide lamps were used extensively in slate, copper and tin mines, but most have now been replaced by electric lamps. Carbide lamps are still used by some cavers exploring caves and other underground areas. They were also used extensively as head lights in early automobiles, though in this application they are also obsolete, having been replaced entirely by electric lamps.
It is still used in the Netherlands and Belgium for a traditional custom called Carbidschieten (Shooting Carbide), and in toy cannons (see Big-Bang Cannon.)
Together with calcium phosphide, calcium carbide is used in floating, self-igniting naval signal flares (see Holmes' Marine Life Protection Association).
Calcium carbide is also used in small carbide lamps called carbide candles, which are used for blackening rifle sights to reduce glare. These "candles" are used due to the sooty flame produced by acetylene.